Localising Median Neuropathies: The Role of Different Investigations.

Answer: B A 50-year-old male with diabetic nephropathy and renal failure on maintenance haemodialysis through a left arterio-venous fi stula was referred to the Neuroscience Clinic with pain, numbness and tingling over the lateral 3 fi ngers of the left hand of a few days duration. The pain increased when the fi stula was used for haemodialysis. On clinical examination, the patient was unable to oppose the thumb and fl ex the thumb, Digit I and Digit II. He also had weakness of wrist fl exion and forearm pronation, suggesting a proximal median neuropathy. Electrodiagnostic studies (Table 1) indicated a mixed axonal and demyelinating sensori-motor polyneuropathy. Additionally, the median nerve study on the right was compatible with a median neuropathy at the wrist. Studies on the left, however, were consistent with a severe median neuropathy with absent sensory nerve action potential and markedly decreased compound muscle action potential. Distal latency to the fl exor pollices longus on proximal stimulation was prolonged indicating a left-sided proximal median neuropathy. Which investigations can assist in localising the site of the left median nerve lesion? Which investigation is most useful? A. Needle electrode examination B. High resolution sonography C. Magnetic resonance imaging (MRI) D. Angiogram E. Serial nerve conduction studies